I just started using Khan Academy with my 15 year old for Algebra. He has always struggled in math and this is the first thing I've found that he doesn't mind using. Because of his age, I keep grades for him. I am trying to figure out the best way to do that with Khan Academy. I am giving him a grade for classwork each day just for practicing skills but I'm not sure how to quiz and test him periodically since Kahn Academy seems to jump around some. Suggestions would be appreciated.

Khan Academy now has Math available for school-aged kids, right through to pre-college level. Not the Science, but as you're only worried about your DS's Math, have a look into Khan now to see if it'll fit. They have worksheets and tests, and you can track your child's progress.

I teach 11 to 16 Science and Maths and having looked at KA I think it's dreadful. In one video about atomic structure, the speaker launched straight into the philosophy of atomic theory. Most of my learners can't even spell 'philosophy' let alone know what it means. I've looked at a lot of material on KA and it's hard to believe any of the authors have ever taught in a regular high-school or similar.

I've been tasked with creating online learning material for Science and Maths and KA has taught me how NOT to do it.